By Dr. Victoria Verdú (Licensed Gynaecologist No. 282847366).
Carrying a pregnancy to term is an extremely complex process for the human body. Numerous physiological and hormonal changes occur, intricately coordinated to ensure that the entire process unfolds smoothly, ultimately giving rise to new life.
Hormones play a fundamental role—not only are they essential for achieving pregnancy, but they also sustain and protect it, ensuring it progresses successfully to term.
In Spain, it is estimated that between 5% and 10% of women of reproductive age may experience difficulties conceiving due to hormonal imbalances. When a woman becomes pregnant, her body begins producing a series of hormones that perform essential functions. The most important ones include:
This is one of the first hormones to appear after fertilization. Produced by the embryo, its main function is to maintain the corpus luteum in the ovary. hCG is widely recognized, as it is the hormone detected by pregnancy tests to confirm conception.
This hormone is responsible for maintaining the endometrium (the inner lining of the uterus) in optimal conditions to receive the embryo. It also inhibits premature uterine contractions and prepares the mammary glands for breast milk production. Progesterone is initially produced by the corpus luteum, but from the end of the first trimester onward, the placenta takes over this function.
These hormones promote uterine growth and support breast development. They also play a role in regulating the maternal immune system, preventing it from rejecting the fetus as a foreign body.
This hormone increases the availability of glucose and fatty acids for the fetus by altering maternal metabolism. It also contributes to breast development.
Crucial during labor, relaxin is responsible for relaxing the pelvic ligaments and softening the cervix to facilitate childbirth. It also participates during early pregnancy by aiding in embryo implantation and increasing blood flow to the uterus.
These hormones become more prominent during labor and lactation, though their levels begin to rise during pregnancy. Oxytocin stimulates uterine contractions, while prolactin prepares the mammary glands for milk production.

Hormonal imbalances during pregnancy can have consequences for both mother and baby. Recognizing warning signs is not always straightforward, but several clinical indicators may suggest that something is amiss. Examples include:
Consequently, if any of these symptoms occur, it is crucial to consult a reproductive medicine specialist or gynecologist.
Hormonal imbalances can pose significant barriers to achieving natural conception. The most common of these is polycystic ovary syndrome (PCOS), which can disrupt ovulation and thus prevent pregnancy. Progesterone deficiency can also occur, resulting in inadequate preparation of the endometrium to receive the embryo.
Other frequent hormonal disturbances include hypothyroidism and hyperthyroidism, both of which can negatively affect embryonic development, as well as hyperprolactinemia (elevated prolactin levels), which may inhibit ovulation.
Human chorionic gonadotropin (hCG) appears in the blood and urine just days after fertilization, around the time of embryo implantation. Therefore, its presence enables pregnancy tests to determine whether a woman is pregnant.
Urine tests can detect hCG at minimal levels, while blood tests can quantify it precisely, providing more detailed information about the progression of pregnancy. hCG levels typically double every 48-72 hours during the early weeks of gestation, and monitoring these levels can be key to confirming that the pregnancy is advancing as expected.
Hormonal imbalances can hinder assisted reproduction treatments. Correcting and controlling these imbalances can improve the likelihood of achieving pregnancy. For this reason, as part of the treatment process, reproductive medicine specialists may recommend preliminary therapies to address such imbalances.
Pharmacological intervention is not always necessary; sometimes, lifestyle modifications—such as quitting smoking or losing weight—may suffice. In other cases, ovulation may need to be stimulated with medication, such as clomiphene citrate, or with gonadotropin (FSH) injections. Progesterone supplementation may also be offered to address progesterone deficiencies.
All of these decisions must be based on sound medical judgment, and only healthcare professionals can recommend the most appropriate treatment after thoroughly evaluating each individual case.